This invention relates to rotary piston mechanisms and more particularly, to such a mechanism for internal combustion engines, fluid motors, pumps and the like, wherein a rotating piston or rotor captured in a chamber moves eccentrically with respect to an output or an input drive shaft emanating therefrom.
Rotary piston internal combustion engines exemplified by the Wankel type engine have a generally triangular shaped rotor in an epitrochoidal chamber. The rotor is eccentrically driven in the chamber as it rides eccentrically about a fixed centrally located gear. Thus, the output drive shaft connected to the rotor is driven at the same rotation rate as the rotor. The three points of the rotor are equipped with sliding seals that engage the inner walls of the chamber and divide the chamber into three spaces, each bounded by one of the faces of the rotor. During a complete revolution of the rotor, each of these spaces moves around the chamber increasing the decreasing in size to perform the four functions of intake, compression, power and exhaust as a gasoline, air mixture is drawn into the space, compressed, combusted to deliver power as it expands, and then finally, exhausted. These functions are performed in all the moving spaces during each rotation of the rotor in the chamber and the power function is performed consecutively in the spaces, always along the same portion of the walls of the chamber. The other functions are also performed consecutively in each of the spaces and each of them is also performed along a given portion of the walls of the chamber. Thus, the combustion and exhaust functions which inflict the greatest wear on the walls of the chamber, occur repeatedly along the same portions of the chamber walls and so, the effectiveness of the seals carried at each of the points of the rotor are inclined to degrade along these portions of the chamber walls.
It is intrinsic to the Wankel type engine and to any type rotary piston mechanism that uses a triangular shaped rotor which seals against the chamber walls at the points of the triangle, that the chamber be epitrochoidal with two symmetrical cusps. Hence, with respect to the axis of the chamber, the walls of the chamber are curvilinear and concave at all points except at the two cusps. At that point, the walls are generally convex with respect to the chamber axis. Hence, the seals must follow a concave wall which changes abruptly to convex at two points along a complete cycle of travel of the seal against the wall and so the angle the seal subtends with the wall is not constant during the entire travel of the seal along the wall. In fact, that angle becomes exceedingly acute as it moves along the wall from a convex portion of the wall to a concave portion. The effectiveness of the seal where the angle is exceedingly acute, is diminished and the seals have a tendency to leak at such points.
Another rotary piston mechanism in which some of the disadvantages of the Wankel type mechanism are avoided is disclosed in our copending U.S. patent application Ser. No. 445,930, entitled Rotary Piston Mechanism, filed Feb. 26, 1974, and now U.S. Pat. No. 3,996,901. A similar mechanism is also described in U.S. Pat. No. 3,285,189 which issued Nov. 15, 1966 to C. Doyer and is entitled Motor, Pump or Compressor with a Piston Rotatable Within the Housing. Both our copending application and the Doyer patent describes an oblong rotary piston or rotor in a generally triangular shaped chamber defined by three equal curved walls that are convex with respect to the chamber axis. Each side of the rotor conforms generally to the chamber wall and the rotor is rotatably mounted so that it rotates about its geometric center and the geometric center moves around the chamber axis over a three cusp epicycloidal path. For each cycle of rotation of the geometric center of the rotor around the chamber axis along the epicycloidal path, the rotor rotates one-half cycle on its geometric center and so the rotor closes successively with the three walls of the chamber six times for each full revolution of the rotor. Furthermore, seals at the ends of the rotor which slide along the walls of the chamber can at all times contact the walls perpendicular thereto.
In Doyer, the chamber is closed at the ends by fixed plates. The plates are fixedly attached to an annular part that defines the chamber and relatively large central openings are provided in the plates to which shafts and axles extend for carrying the rotor and for delivering a shaft output from the rotor. With this construction, it is required that the width of the rotor be relatively large because it must cover these large central openings in the plates even when the rotor is in an extreme position against one of the chamber walls. In other words, the width of the rotor must be substantially greater than the shortest distance from the chamber axis to one of the chamber walls. Thus, it is intrinsic in Doyer that the area of the rotor must be more than half the area of the chamber. This, of course, limits the intake volume for a fixed chamber size.
In our U.S. Pat. No. 3,996,901, the above described limitation of Doyer is avoided by providing rotating end plates that connect directly to the output shaft and which carry the rotor on an axle which is eccentric with respect to the output shaft. Hence, there are no central openings through the ends of the chamber which must be covered by the rotor. Furthermore, the rotating end plates contain intake and exhaust holes which come into registration with fixed intake and exhaust holes in the mechanism housing. This enables a two cycle type of operation with six power strokes for each revolution of the rotor about its geometric center. Such operation is not possible in Doyer which provides only two power strokes for each revolution of the rotor about its geometric center.
The present invention discloses an improvement in the rotary piston mechanism described in our U.S. Pat. No. 3,996,901. More particularly, the present invention provides a gear train carried by at least one of the rotating chamber end plates that carries the rotor for rotating the rotor on the rotor axis (geometric center). Thus, the rotor position and attitude is totally controlled by connections to and through the rotating end plate, and, therefore, independent of contact with the chamber side walls.